Method for coating fasteners

ABSTRACT

A method and apparatus for coating a fastener, particularly a fastener with a head portion and shank portion, with a coating material is provided. The invention includes the steps of and apparatus for supporting the fasteners such that the fasteners are positioned for coating. The fasteners are conveyed such that the fasteners are moved through a plurality of operation stations and pass through a heating station where the shank portions of the fasteners are heated. Subsequently, at a material applying station, a coating material is applied to the heated shank portions. A preferred embodiment of the method and apparatus of the present invention includes supporting the fasteners on their head portions with the shank portions projecting upward, conveying the fasteners with their shank portions projecting upward for processing, heating the shank portion to a temperature above the melting point of the applied material and applying the material to the heated shank portion to form a coating thereon.

TECHNICAL FIELD OF THE INVENTION

This invention relates to a method for coating fasteners and moreparticularly to an improved method for coating fasteners, having shankand head portions, with a powder material.

BACKGROUND OF THE INVENTION

Numerous methods and devices have been employed in the past for coatingfasteners. Some of these methods and devices are useful in coatingcertain types of fasteners, but are not as versatile as may be necessaryto coat other types of fasteners.

Examples of such methods and devices include U.S. Pat. No. 3,452,714 inthe names of G. F. C. Burke, Richard J. Duffy et al., U.S. Pat. No.4,120,993 to Richard J. Duffy et al., and U.S. Pat. No. Re. 28,812 toRichard J. Duffy, one of the present inventors. The methods and devicesdisclosed in these United States Patents provide for the coating offasteners in which the shank portion of the fastener depends below apair of traveling belts. The fasteners are supported on the belts attheir head portion. These methods and apparatus prove very efficient forcoating fasteners which are void of projections depending downwardlyfrom the head portion of the fastener, since such fasteners may bepositioned with the shanks between the belts and remain in a stableposition for coating. However, these methods and apparatus provesomewhat inefficient and less versatile than required when fastenersincluding projections depending downwardly in the direction of the shankportion are to be coated as well as rotated during the coating process.Fasteners including such projections are not readily placed in a stableposition with their shank portions projecting downward between the beltsand can not be easily and efficiently coated in this configuration.Furthermore, the methods and apparatus of the previously describedpatents do not provide the ability to precisely control the linear speedand rotation of the fasteners during the coating process.

Thus, it would be advantageous to provide a method and apparatus whichcoated a large variety of fasteners, including fasteners havingprojections depending downwardly from the head portion of the fastener,in a cost efficient, versatile and continuous manner. Further, it wouldbe advantageous to provide a method and apparatus which wouldautomatically and rapidly coat a wide variety of fasteners, includingthose fasteners having projections depending downwardly from their headportion.

It would also be advantageous to provide a method and apparatus whichaccommodates a variety of fastener sizes and which could be quickly andeasily adapted for coating various sizes of both male and femalefasteners. In addition, it is desirable to provide a method andapparatus which has the versatility to coat a specified portion of thethreads of the fastener, as well as the complete threaded area, andfurther, a method and apparatus which may coat only a specific portionof the radial distances about the threaded surface of the fastener.Furthermore, it would be advantageous to provide a method and apparatuswhich provides the ability to precisely control the linear speed androtation of the fasteners to be processed in both a shank up as well asa shank down orientation.

SUMMARY OF THE INVENTION

In accordance with the present invention, a method for coating one ormore fasteners having head and shank portions with a powder material isprovided. The method includes the steps of supporting the fastener forprocessing and heating the shank portion to a temperature above themelting point of the powder material to be applied. The method alsoincludes the step of applying the powder material to the heated shankportion of the fastener to coat the fastener.

In a preferred embodiment of the method of the present invention, thefastener to be processed is rotated at least 360 degrees while thepowder material is being applied to the heated shank portion of thefastener. This may be effected by subjecting the fastener to a magneticfield during application of the powder material to increase the dragimparted to the fastener thereby causing its controlled positiverotation. Further, a preferred embodiment of the present method alsoincludes the step of collecting powder material which is not applied tothe fastener during application of the powder material. This appliedpowder is collected and reused for future coating applications.

In applying the powder material, a preferred method contemplatesspraying the powder material on the heated shank portion of thefastener. In order to provide 360 degree coverage of at least a portionof the shank, the powder material is sprayed from at least two spraylocations spaced from one another. Another preferred method contemplateslinearly conveying the fasteners supported on their head portions withthe shank portions projecting upward.

The apparatus practicing the method of the present invention provides amember for supporting the fasteners for coating. A conveying member isalso provided to controllably advance the fasteners during coating. Aheating element is provided for heating the fastener as well as amaterial applicator for applying the material to the fastener.

In a preferred embodiment, the apparatus also includes a cooling stationfor cooling the heated fasteners which may also include a rustpreventative to maintain the quality and finish of the coated fasteners.Further, the supporting member may include a linearly travelingconveying member and more preferably a pair of endless traveling beltswhich are supported throughout a major portion of their length and onwhich the head portion of the fastener rests. In order to provide a 360degree coating on the fastener and to effect rotation of fastenersduring the coating operation, a preferred embodiment of the apparatusmay include one of the pair of traveling belts having a coefficient offriction less than the other belt, the belts being movable in the samedirection at different speeds and/or the belts being movable in oppositedirections at various speeds. Furthermore, in a preferred embodiment,one belt of the pair of belts may be wider than the other and one of thebelts may be provided with cradle members to effect the desiredsupporting and conveying characteristics. Moreover, it may be desirableto provide belts which are adjustable such that at least one of thebelts is positionable with respect to the other to accommodate a varietyof fastener sizes, including a plurality of fastener head and shankportion sizes and shapes.

Thus, the invention provides the versatility for coating a wide varietyof fasteners, including those fasteners having projections dependingfrom the head portion of the fastener, which have previously beendifficult to coat. The present invention provides a simple, rapid,inexpensive method and apparatus for coating a wide variety offasteners, including those fasteners having projections dependingdownward from their head portion which require that the fastener besupported on their heads with the shanks projecting upwardly to ensure aproper and uniform coating process.

These and other advantages of the present invention will become apparentto those skilled in the art from the detailed disclosure of the presentinvention as set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth in the appendedclaims. The invention itself, however, together with further attendantadvantages thereof, will be best understood by reference to thefollowing description taken in conjunction with the accompanyingdrawings in which:

FIG. 1 is a block diagram illustrating the steps of the presentinvention;

FIG. 2 is a perspective view of one embodiment of the apparatus of thepresent invention;

FIG. 3 is an enlarged perspective view of a portion of the apparatus ofFIG. 2 illustrating the fastener, as it is being coated with powdermaterial;

FIG. 4 is a cross-sectional view taken along line 4--4 of FIG. 3illustrating the relationship between the pair of belts conveying thefasteners; and

FIG. 5 is an enlarged, explode perspective view of the apparatus of FIG.2 illustrating the belt conveying and adjusting mechanism.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in relation to coating studswhich include a head portion, a shank portion and a plurality ofprojections depending downwardly from the head portion parallel to thecentral axis of the shank portion. However, it is to be understood thatthe present invention is useful in coating a variety of fasteners,including, but not limited to, screws, bolts, studs and similarexternally threaded articles. Furthermore, it may be appreciated bythose skilled in the art that the present invention may have advantagesand may be used to provide a coating on a wide variety of internallythreaded articles including, but not limited to, nuts, collars and thelike.

The present method and apparatus may also be used to apply a variety ofcoatings to fasteners. Such coatings include, but are not limited to,non-conductive coatings, lubricating coatings, a combination of bothnon-conductive and lubricating coatings as well as similar types ofcoatings. Furthermore, such coating materials may include, but are notlimited to, thermoplastic or thermosetting materials. Specifically, suchcoatings may include, but are not limited to nylon, acrylic, as well asfluorocarbon and polyethylene based materials. An example of such amaterial is manufactured by Du Pont Corporation and is distributed underthe trademark Teflon-P.

As shown in the block diagram of FIG. 1, a method of coating a fastenerhaving a head and shank portion with powder material includes the stepsof supporting the fastener as illustrated at step 10. As may appreciatedby those skilled in the art, the fastener may be supported on its headportion such that the shank portion projects upward away from thesupporting structure or downward through the supporting structure. Forthe purposes of illustration only, the present invention will bedescribed with the fastener being supported on its head portion with theshank portion projecting upward away from the supporting structure.

The fasteners are conveyed with the shank portions projecting upward forprocessing at step 12. At step 14, the shank portions of the fastenersare preferably heated to a temperature above the melting point of thepowder material and the powder material is applied to the heated shankportion of the fastener at step 16. As further illustrated in FIG. 1,the method of the present invention may include the step of collectingthe powder material which is not applied to the fastener at step 16.Accordingly, the overspray of powder material may be collected and usedfor subsequent processing at step 18.

The overall method of coating, as well as the specifics relating to themethod, will be described in conjunction with the exemplary apparatusillustrated in FIGS. 2 through 5. It will be understood by those skilledin the art that additional and/or modified apparatus, other than thespecific apparatus shown herein, may be used to carry out and practicethe present invention. Furthermore, it will be understood by thoseskilled in the art that the method of the present invention may also bepracticed in the instance where individual fasteners may be coated insingle station test apparatus or by hand. For the purposes ofillustration only, the present invention will also be described inconjunction with the coating of weld studs, but it should be understoodthat a wide variety of fastener types may be coated by and enjoy theadvantages of this invention.

As illustrated in FIGS. 2, 3 and 4, an apparatus supported by frame 19is provided to continuously and automatically coat weld studs 20 with apowder material. Such studs include head portions 22 and shank portions24 as well as a plurality of projections 26 depending downwardly fromthe head portions. The apparatus is controlled at control panel 27 andincludes a feeding station 29 at one end of the machine for feeding thefasteners onto a supporting member with the shanks of the fastenersdirected upward. The supporting member is provided to support thefasteners in a stable position for coating. Specifically, the fastenersare positioned on their head portion 22 with the shank portion 24projecting upward and away from the supporting member. As illustrated,the supporting member may include a pair of endless traveling belts 28Aand 28B which are supported throughout a major portion of their lengthby support members 30A and 30B. Belt 28A moves at speeds in the range ofabout 0.67 inches per second to about 6.7 inches per second. Belt 28Bmoves at speeds in the range of about 0.67 inches per second to about33.5 inches per second. The belt speeds are varied within these rangesto obtain the desired processing rate and, in part, rate of rotation.Head portion 22 of the fasteners rest on both belts 28A and 28B andallows the fasteners to remain in a stable position for coating.

To add to the versatility and advantages of the present invention one ofthe pair of belts may be wider than the other. As illustrated, belt 28Ais the wider belt and is about 0.50 inches to about 1.5 inches wide andmore preferably 0.75 inches to about 1.0 inch wide. The smaller belt 28Bis about 0.18 inches to about 1.0 inch wide and more preferably 0.25inches to about 0.50 inches wide. As may be appreciated by one skilledin the art, various belt widths may be used depending on the type andsize of the fastener to be processed.

Furthermore, it may be desirable to provide rotation of fasteners 20during at least a portion of their processing. To this extent, one ofthe pair of belts may have a coefficient of friction less than the otherof the pair. This allows the belt with a higher coefficient of frictionto provide a surface which engages the head of the fastener to a greaterextent than the belt with the lower coefficient of friction. To maintainsuch coefficients of friction, belt 28A may be a glass belt impregnatedwith teflon to lower its coefficient of friction. Belt 28B may be aglass belt impregnated with silicon, thereby creating a highercoefficient of friction as compared with belt 28A. As may beappreciated, other types of material may be used for belts 28A and 28Band still provide the differential in coefficients of friction.

As illustrated in FIGS. 2, 4 and 5, belts 28A and 28B may be completelyadjustable with respect to one another, such that adjustment may beeffected in height as well as the width. This provides an apparatuswhich will accommodate a plurality of fastener sizes, including a widevaiety of head and shank portion diameters as well as add versatility inpositioning the fastener for coating.

An example of such an arrangement is illustrated in FIG. 5 and ispositioned on either end of the apparatus. Adjustability of the belts isprovided through pulleys and 32A and 32B located at either end of theapparatus on which belts 28A and 28B ride, respectively. Each pulley 32Aand 32B rides on shaft 34 and may be adjusted along the shaft and lockedthereto through set screws 36A and 36B. Shaft 34 rides in apertures 38and 40 in frame members 42 and 44. Bushing assemblies 46 and 48 secureshaft 34 to frame members 42 and 44 and may provide some adjustment ofthe shaft. Bolts 50 secure bushings 46 and 48 to frame members 42 and44, while bolts 52 provide integrity of the frame structure of theapparatus. It may be appreciated that a variety of adjusting structuresmay effect the advantages of the present invention and may include, butare not limited to, adjusting support members 30A and 30B on which belts28A and 28B ride.

As illustrated in FIG. 4, adjusting one belt higher than the otherallows the fastener to be angularly positioned with respect to thecoating station to aid in rotation and application of the coatingmaterial. It has been determined that a height differential of aboutbetween 0.010 inches and 0.125 inches is operable, while a heightdifferential of about between 0.030 inches and 0.100 inches ispreferable. As may be appreciated, this differential may vary dependingon the size and type of fastener to be coated.

Adding to the flexibility of the present invention, belts 28A and 28Bmay be moved at different speeds and may also be moved in directionsopposite to one another to provide rotation of the fasteners eitheralone or in combination with providing differential coefficients offriction for each belt. As may be appreciated by one skilled in the art,a variety of conveying methods may be employed to convey the fastenersin a linear fashion with their shank portions projecting up and down.Such methods, include but are not limited to, belts, platforms, arms andsimilar linear conveying structures.

As further illustrated in FIGS. 2, 3 and 4, the fasteners 20 areconveyed during movement of belts 28A and 28B, with shank portions 24projecting upward away from the belt supports. As shown, the conveyingmember is illustrated as a cradle member 54 which is attached to belt28A. Cradle member 54 includes perpendicular arms 56 and 58 which form areceiving area for head 22 of fastener 20. These arms provideperpendicular positioning of the fasteners with respect to the directionof the travel of belts 28A and 28B. Arm 56 functions as a retainingmember, while arm 58 functions as the carrying surface, which providesthe down line momentum for the fastener during processing.

Cradle members 54 are attached to the wider belt 28A through rivets 60and are spaced equally along belt 28A, as shown in FIG. 3. Preferably,the spacing of cradle members 54 will be at least as wide as, and may beslightly larger than, the largest dimension of the head of the fastener.As may be appreciated, this spacing will vary with the size and type offastener to be coated. It may be appreciated that while cradle member 54is shown as attached to belt 28A, it may be advantageous in someinstances to attach cradle members to both belts 28A and 28B. However,in the instance where it is desirable for the belts to move in oppositedirections, such dual connection is not maintained. In the preferredembodiment illustrated in FIGS. 2, 3 and 4, a plurality of cradlemembers 54 are provided in a spaced relationship along traveling belt28A. The cradle members accept and carry the head portions of fasteners20 and provide downline movement of the fasteners for furtherprocessing. The downline movement provided by cradle members 54 iscontrolled such that the rate of advancement and rotation of thefasteners is easily adjusted and can be precisely determined.

As fasteners 20 move downline, they move through a plurality ofoperating stations. Specifically, the shank portions of the fasteners,which are projecting upward from belts 28A and 28B, move toward andthrough a first operating station having a heating element 62 whichheats shank portions 24 of fasteners 20. As may be appreciated, avariety of heating elements may be utilized. Such heating elementsinclude, but are not limited to, induction heaters, ultrasonic heaters,infrared heaters, furnaces and similar heating devices. In the preferredembodiments illustrated in FIG. 2, an induction generator 64 andassociated heating coil 66 are provided. Such a heating element ispreferred to efficiently heat the metallic fasteners passing throughheating coil 66. In order to exhaust any residue vaporized duringheating of the fasteners, vacuum port 68 is provided on one side ofbelts 28A and 28B.

In carrying out the present invention, fastener shank portions 24 areheated to a temperature in a range to provide flow of the material to beapplied to the fastener to coat the fastener in a satisfactory manner.For example, in application of Teflon powder the temperature range isfrom about 570 degrees Fahrenheit to 1000 degrees Fahrenheit, and morepreferably, from about 750 degrees Fahrenheit to about 850 degreesFahrenheit. Specifically, this temperature range provides a heatedfastener shank sufficiently above the melting point of the Teflon powdermaterial and provides an acceptable coating when applied. Generator 62includes a variable power setting which allows adjustment of thepoweroutput of the generator to accommodate the desired fastenerproduction rate. It may be appreciated by one skilled in the art, that avariety of machine parameters may be modified to attain acceptable andworkable results when using the apparatus described herein as anexemplary embodiment of the present invention. Accordingly, the machineparameter ranges disclosed herein are by way of example only and are notintended to limit the present invention.

As fasteners 20 move downline from the heating station, they move to andthrough the powder application station in the exemplary embodiment ofFIGS. 2 and 3. Specifically, the fasteners pass between a spray nozzle70 on one side of belts 28A and 28B and a vacuum port 72 on the oppositeside of belts. Coating material is supplied from reservoir 74, throughconduit 76 to spray nozzle 70. As illustrated in FIG. 3, conduit 76 isattached to spray nozzle 70 through a nut 78 which terminates in a tube80 to feed the powder to spray nozzle 70.

In order to spray the coating material on the fasteners, spray nozzle 70is approximately 5.5 inches wide and 7.0 inches long and is positionedsuch that it sprays coating material across belts 28A and 28B and acrossthe line of travel of fasteners 20. Vacuum port 72 collects anyoverspray of he coating material not applied to the fasteners. Thedistance between spray nozzle 70 and vacuum port 72 is adjustable andgenerally is about 1 inch and about 10 inches, and more preferablybetween about 2 inches and about 4 inches. As may be appreciated bythose skilled in the art, distance between spray nozzle 70 and vacuumport 72 may vary according to the size and type of fastener to becoated.

The powder application station illustrated in FIGS. 2 and 3 may besimilar to those disclosed in U.S. Pat. No. 3,579,684 to Richard J.Duffy. Such stations may include nozzles formed as flattened ends oftubular members secured to one end of a tubular manifold, includinginlets for supplying gas under pressure to the manifolds and inletsthrough which plastic particles are introduced. A metered powder supplymay be used to supply powder to conduits leading to the inlets as wellas to the manifolds. Such a device may be arranged with a movable guidesuch that the powder may be directed relative to the entrance of theconduit such that one or more conduits may be supplied to provide one ormore powder application stations. Particularly, spray nozzle 70 is afan-shaped nozzle having an aperture which is in the range of aboutbetween 0.06 to about 0.25 inches wide by about 4 to about 7 incheslong. As illustrated in the preferred embodiment of FIG. 2, spray nozzle70 may be disposed at angle with respect to the axis of the shankportion of the fastener as well as at an angle with respect to thedirection of travel of the belts.

When it is desired to provide a non-conductive coating on fasteners 20,it may be desirable to apply the coating material on shank portion 24 offasteners 20 such that the material completely encircles a portion, andmore preferably, the complete shank portion 24 of the fasteners. Inorder to accomplish this result, the apparatus of the present inventionmay provide for rotating the fastener shank portion at least onecomplete revolution during processing as described above. Such rotationmay take place while applying the coating material at the powderapplication station. While at least one complete revolution of thefastener provides 360 degree coverage, it may be desirable to rotate thefastener more than one complete revolution during application of thecoating material. Accordingly, it may be preferred to rotate thefastener as many as seven (7) to nine (9) rotations during applicationof the coating material.

One such method of rotating and/or aiding rotation of the fastenersincludes providing a magnetic field which is imparted on the fastenersduring processing, and more particularly, during the application of thepowder material at the powder application station. Such a magnetic fieldincreases the drag on a portion of the fastener aiding and/or providingrotation of the fastener. As illustrated in FIGS. 3 and 4, a pluralityof equally spaced magnets 82 are embedded in support member 30B belowbelt 28B. Magnets 80 span the length of travel of fasteners 20 betweenthe powder application station and may include, but are not limited to,a single strip magnet, a plurality of individual magnets, and similarmagnetizing structures which may include an electromagnetic source. Asillustrated in FIGS. 2 and 3, this length is that portion of theapparatus between the end of induction heating coil 66 and the end ofthe spray nozzle 70.

The apparatus of the present invention also includes means for removingthe coated fasteners from the processing apparatus. This is illustratedas a cam member 82 which directs the processed fasteners out of cradle54 to a discharge chute 84. At this point, the fasteners fall through adischarge conduit and are deposited into cooling tank 88. Fasteners 20are cooled in tank 88 then packaged for subsequent shipment. A coolingtank 88 includes a cooling liquid and may also preferably include a rustinhibiting additive to prevent surface corrosion of the fasteners.

A second preferred embodiment of the present invention (not illustrated)includes apparatus imilar to that of FIGS. 2 and 3, but includes analternative apparatus for applying the powder material from oppositesides of the fastener shank portion to effect complete 360 degreecoverage of a predetermined portion or all of shank 24. This sprayingarrangement includes at least two spraying stations which direct coatingmaterial from 180 degree opposite locations on either side of belts 28Aand 28B. Such a configuration also provides 360 degree coating offastener shanks 24 which may or may not be rotated as described above.As may be appreciated by one skilled in the art, this type of opposedspraying operation may take place at one or more operating stationsdownline of the heating operation.

Accordingly, a cost efficient, continuous method and apparatus forcoating fasteners is disclosed. This type of apparatus and method willprovide versatile coating of a wide variety of fasteners, including bothmale and female fasteners as well as fasteners including projectionsdepending downward from the head of the fasteners.

We claim:
 1. A method of coating a fastener having a head portion andshank portion with a material comprising the steps of:supporting thefastener for coating; controllably advancing the fastener for coating;heating the shank portion of said fastener to a temperature above themelting point of said material; applying said material to the heatedshank portion of said fastener; and controllably rotating the fastenerat least 360 degrees during application of said material to coat theentire circumference of at least a segment of said shank portion withsaid material.
 2. The method of claim 1 wherein the step of rotatingsaid fastener includes applying a magnetic field in the presence of saidfastener during application of said material to at least aid in rotationof said fasteners.
 3. The method of claim 1 including the step ofcollecting said material not applied to the fastener during the step ofapplying said material.
 4. The method of claim 1 wherein the step ofapplying said material includes spraying the material on the heatedshank portion of said fastener from at least two spray locations spacedfrom one another to effect a 360 degree coating on at least a segment ofsaid fastener shank portion.
 5. The method of claim 1 including the stepof linearly conveying said fastener with said shank portion projectingupward.
 6. A method of coating a fastener having a head portion and ashank portion with a material comprising the steps of:supporting thefastener for coating; controllably advancing the fastener for coating;heating said shank portion of said fastener to a temperature above themelting point of said material; applying said material from at least onespray location to the heated shank portion of said fastener; andcontrollably rotating said fastener during application of said materialincluding the application of a magnetic field in the presence of saidfastener, also during application of said material, to at least aid inrotation of said fastener so as to coat a predetermined circumference ofat least a segment of said shank portion with said material.
 7. Themethod of claim 6 wherein said step of controllably rotating saidfastener includes controllably rotating said fastener at least 360degrees during applicaton of said material.
 8. The method of claim 6wherein the step of supporting the fastener for coating includessupporting the fastener on said head portion with said shank portionsprojecting upward.
 9. A method of coating a fastener having a headportion and a shank portion with a material comprising the stepsof:supporting the fastener for coating with the fastener positioned ontwo endless moving belts, one belt having a higher coefficient offriction than the other; controllably advancing the fastener for coatingthrough movement of said endless belts; heating said shank portion ofsaid fastener to a temperature above the melting point of said material;applying said material from at least one spray location to the heatedshank portion of said fastener; and controllably rotating said fastenerat least 360 degrees during application of said material through varyingthe speed of said moving belts so as to coat the entire circumference ofat least a segment of said shank portion with said material.
 10. Themethod of claim 9 wherein the step of controllably rotating saidfastener includes moving said moving belts in opposite directions torotate said fastener so as to coat the entire circumference of at leasta segment of said shank portion with said material.